.TH LOMB 1 "16 June 2003" "WFDB 10.3.8" "WFDB Applications Guide"
.SH NAME
lomb \- estimate power spectrum using the Lomb periodogram method
.SH SYNOPSIS
\fBlomb\fR [ \fIoptions ...\fR ] \fIinput-file\fR
.SH DESCRIPTION
.PP
\fBlomb\fR transforms a real-valued time series (from the specified
\fIinput-file\fR, or from the standard input if \fIinput-file\fR is
specified as "-"; \fIinput-file\fR must be in text form) into a
power spectrum (on the standard output), using a technique known as
the Lomb periodogram.
.PP
The input is a text file containing a sampled time series, presented
as two columns of numbers (the sample times and the sample values).
The intervals between consecutive samples need not be uniform (in
fact, this is the most significant advantage of the Lomb periodogram
over other methods of power spectral density estimation).  \fBlomb\fR
writes the Lomb periodogram (the power spectral density estimate
derived from the input time series) on the standard output, in two
columns (frequency and power).  If the units of the sample times in the
input file are seconds, the units of the frequencies in the output are Hz.
.PP
\fIOptions\fR are:
.TP
\fB-h\fR
Print a usage summary.
.TP
\fB-P\fR
Generate a power spectrum (print squared magnitudes).
.TP
\fB-s\fR
Smooth the output.
.TP
\fB-z\fR
Add a constant to each input sample, chosen such that the mean value of the
entire series is zero.
.PP
Among many other applications, this program can be used to estimate
heart rate power spectra, in combination with \fBihr\fR(1).  The Lomb
method is ideal for analysis of any time series with missing or noisy
data (the noisy data may be removed from the time series and need not
be replaced, as would be necessary if conventional PSD estimation
algorithms were employed).
.SH SEE ALSO
\fBfft\fR(1), \fBhrfft\fR(1), \fBmemse\fR(1)
.HP
Lomb, N.R.
Least-squares frequency analysis of unequally spaced data.
\fIAstrophysics and Space Science\fR \fB39\fR:447-462 (1976).
.HP
Press, W.H, and Rybicki, G.B.
Fast algorithm for spectral analysis of unevenly sampled data.
\fIAstrophysical J.\fR \fB338\fR:277-280 (1989).
.HP
Press, W.H. Teukolsky, S.A., Vetterling, W.T., and Flannery, B.P.
\fINumerical Recipes in C: the Art of Scientific Computing\fR, pp. 575-584
(Cambridge Univ. Press, 1992).
.HP
Moody, G.B.
Spectral analysis of heart rate without resampling.
\fIComputers in Cardiology 1993\fR, pp. 715-718
(IEEE Computer Society Press, 1993).
http://www.physionet.org/physiotools/lomb/lomb.html .
.SH AUTHOR
George B. Moody (george@mit.edu)
.SH SOURCE
http://www.physionet.org/physiotools/wfdb/psd/lomb.c
